1. Field of the Invention
The present invention relates to a sustained release system, and in particular relates to a sustained release composition containing release rate determined agent.
2. Description of the Related Art
The desirability of coating medical devices such as, surgical implants, sutures and wound dressings with pharmaceutical agents is well known. Such coated devices provide a means for locally delivering pharmaceutical or therapeutic agents at the site of medical intervention to treat a variety of diseases. For example, surgical implants or sutures coated with antibiotics can provide local delivery of antibiotics directly to an implantation or suture site, thereby decreasing the onset of infection following the surgical intervention.
Thus, there is an increasing interest in developing a drug delivery system which is both safe and which provides a high biological availability of the drug, i.e. to maximize pharmaceutical activity of known drugs as well as to minimize the side effects thereof. Due to their uniform release rate during a given time period and the non-toxic property of degradation products, biodegradable polymers have been widely investigated as drug carriers. Biodegradable polymer drug carriers are especially useful for delivering drugs requiring continuous and sustained release with a single administration, e.g. peptide or protein drugs, which should be administered daily because of quick loss of activity in the body.
However, the traditional drug release curve includes three phases with an initial release phase, a lag phase, and a secondary release phase, wherein the drugs are only released at initial and secondary release phases. Thus, at the lag phase, it is necessary to combine an oral administration with the local administration to achieve a desired therapeutic goal, with the additional oral administration increasing costs and causing inconvenience. To overcome the above problems, a novel sustained release composition and manufacturing method thereof are needed.